There is major demand for extended beams that combine low weight with high strength, particularly in the aviation industry. Meter-long beams are made from fiber composite material to support curved structures in aircraft fuselages. These fiber composite beams are given a shape that corresponds to the curved structure. A curvature with a radius of curvature R is thus imparted to the beams along at least a part of the longitudinal extent of the beam.
A male tool against which the fiber composite material is shaped before hardening is used in fabricating curved beams. The male tool can consist of a metal tool with a rectangular cross-section shaped so that a curvature is obtained in the longitudinal direction. The male tool has a first flange/side and a second opposing flange/side, both of which are curved in such a way that the flanges are parallel along their entire extents. One problem associated with the fabrication of curved beams using this type of tool is that it is difficult to get a laminate comprised of layers of fibers with different fiber directions to follow the curvature of the beam when the curvature is large, i.e. the radius of curvature R is small. Using current fabrication methods, the beam is fabricated in that a laminate is applied over the intermediate web and then brought down over the flanges of the tool. This fabrication method gives rise to the formation of folds at the curved surface of the tool that comprises the inner curved surface, i.e. the surface that faces in toward the center of the radius of curvature R. To prevent folds from being formed in a first flange that is formed against the first flange of the male tool, small wedge-shaped pieces of material are cut from the composite layer in that area. However, this entails a major waste of material and degraded strength in the finished beam. Supporting layers can be applied to the slit surface of the beam to mitigate the strength problem. However, one disadvantage of such supporting layers is that they increase the weight of the finished beam, which is undesirable, particularly in an aviation context.